Grout
Also called: tile grout, sanded grout, unsanded grout, epoxy grout
The cement or epoxy filler packed into the joints between tiles after the adhesive cures. Unsanded grout is for joints under 1/8 inch (most backsplashes); sanded for wider joints. Cement grout needs sealing; epoxy doesn't but is harder to work with.
Unsanded cement grout is smooth and packs into narrow joints — the 1/16 to 1/8 inch spacing typical of subway and mosaic backsplashes — without scratching glass or polished stone. Sanded grout has fine sand for strength in joints 1/8 inch and wider; it will scratch glass. Epoxy grout is stain-proof, never needs sealing, and is ideal behind a range, but it sets fast, costs three to four times as much, and is unforgiving for a first-timer. Newer “high-performance” cement grouts split the difference.
Grout goes on 24–48 hours after the tile is set: packed diagonally with a rubber float, excess scraped off, then sponged clean in light passes before it hardens. The joint where the backsplash meets the countertop is never grouted — it moves — and gets color-matched caulk instead.
Cement grout is porous. Seal it 48–72 hours after grouting and again every year or two in a kitchen; unsealed grout behind a stove stains within months.